In a column, such as a distillation or an absorption column, mass transfer is carried out by the upflow of vapor against countercurrent downflow of liquid. In order to enhance the effectiveness of the mass transfer while avoiding a large pressure drop across the column, packing may be employed within the column. The packing may be random packing or structured packing. Structured packing is preferred for more rigorous separations such as the cryogenic distillation of air into nitrogen, oxygen or other atmospheric gases.
Generally structured packing comprises a corrugated sheet of metal or other suitable material. The sheets are vertically oriented within a column with the corrugations at an angle to the column axis. Generally this angle is about 45 degrees. The sheets are stacked within the column side by side such that each sheet has adjacent sheets on which the corrugations are reversed in direction relative to the vertical axis of the column. The height of each stack of packing is generally within the range of from 6 to 10 inches and each stack is placed in the column with the direction of its metal sheets at an angle, generally 90 degrees to the stacks immediately above and below it. The sheets may contain perforations to allow liquid to pass freely onto both sides of the sheets and also to equalize vapor flow in the channels formed between adjacent sheets.
A recent advance in structured column packing is the packing disclosed in U.S. Pat. No. 4,186,159 Huber and in U.S. Pat. No. 4,296,050-Meier. This packing is characterized by fluting on the surface of the corrugated packing sheet. The fluting is a roughening of the sheet surface by grooving or by the impression of a pattern, for example a herringbone pattern, and serves to improve liquid distribution over the sheet surface by capillary action and channelling. The predominant mechanism causing liquid to spread laterally over the packing surface is weak surface tension forces acting along the flutes. The liquid holdup on the packing sheet is relatively small.
Since liquid holdup on the packing sheet will increase the vapor-liquid contact time and thus the mass transfer effectiveness, it is desirable to have structured column packing which enables liquid holdup on the packing surface which exceeds that possible with presently available packing.
Accordingly it is an object of this invention to provide improved fluted structured column packing which enables improved liquid holdup of downflowing liquid along its surface.
It is another object of this invention to provide improved fluted structured column packing which enables increased liquid-vapor contact time for liquid and vapor flowing countercurrently through a given height of packing.
It is a further object of this invention to provide improved fluted structured column packing which enables increased mass transfer through a given height of packing without a significant increase in vapor pressure drop over the given height.